This is the granddaddy of big-leaved perennials. No other plant can so thoroughly alter the scale of a garden while calling such attention to itself. The architectural leaves grow up to 6 feet across. They are rounded and deeply toothed, and sit atop prickly stalks that extend to 10 feet tall and form giant clumps. Gunnera manicata produces large, bottle-brush spikes of tiny reddish-green florets in the spring. It looks particularly at home at the water's edge.